As having good mechanical properties (especially, impact resistance) and electric properties with high transparency, polycarbonate resins are widely utilized as engineering plastics in various fields of OA appliances, electric and electronic appliances, vehicles, building materials, etc.
Of those, OA appliances and electric and electronic appliances require high flame retardancy. For these, therefore, used are polycarbonate resins, which are among various thermoplastic resins, as having a high oxygen index and generally self-extinguishability. In order to further improve their safety in various applications, resin compositions with improved flame retardancy are much desired. Given this situation, therefore, polycarbonate resin compositions comprising halogen-containing compounds as a flame-retardant have heretofore been developed. For example, known are a variety of polycarbonate resin compositions comprising, as a flame retardant, any of halogen-containing compounds such as polycarbonate bromide oligomers and comprising, as a flame retardant aid, Sb.sub.2 O.sub.3 or the like.
Recently, however, halogen-containing compounds such as highly carcinogenic dioxin, which are discharged from waste incinerators, are problematic in that they have bad influences on the environment and human bodies. For this reason, flame-retardant polycarbonate resin compositions not containing any halogen compounds but comprising only non-halogen compounds are much desired.
In addition, the thickness of shaped products of resins is often desired to be small. For their smooth shaping into thin products, resins require not only high flame retardancy but also good flowability.
Prior Art:
As one example of resin compositions satisfying those requirements, known is a polycarbonate resin composition comprising a polycarbonate resin and a styrene-containing graft copolymer, such as an acrylonitrile-butadiene-styrene resin (ABS resin), and containing a non-halogen compound as a flame retardant (see Unexamined Published Japanese Patent Application No. 2-32154). However, the styrene-containing graft copolymer to be in this resin composition is composed of substantially two or more grafting copolymers, and this is expensive. Therefore, it is desired to use any more inexpensive component to produce resin compositions having the same effect as that of the known resin composition.
On the other hand, also known is a resin composition comprising a polymer alloy of a butadiene-free polystyrene and a polycarbonate resin and containing a non-bromine flame retardant (see Unexamined Published Japanese Patent Application No. 62-4746). However, as not containing butadiene, this resin composition has low impact strength and is therefore problematic in its practical use.
Further known is a resin composition comprising a polycarbonate (PC) and an ABS resin and containing talc that acts to improve the stiffness of the composition and to improve the frosted surface appearance thereof (see Examined Published Japanese Patent Application No. 54-33262 and Unexamined Published Patent Application No.4-227650). However, the composition disclosed in the publication is problematic in that its flame retardancy is not satisfactory.
On the other hand, known is a polycarbonate resin composition comprising a polycarbonate resin and a styrene copolymer that acts to improve the flame retardancy and the flowability of the composition, such as an MBS resin, an ABS resin or a BS rubber, and containing a bromine-containing flame retardant, a flame retardant aid and an inorganic substance such as talc (see Unexamined Published Japanese Patent Application No. 54-54165). However, this composition is a halogen-containing one and is against the recent non-halogen requirement. In addition, this composition is problematic in that its heat stability is poor if the butadiene content of the styrene copolymer component therein is not smaller than 50% by weight.